Prediction of discordant twins by real-time ultrasonography combined with umbilical artery velocimetry

Objective: To evaluate the role of umbilical Doppler velocimetry combined with ultrasonographic intertwin differences derived from estimated fetal weight, biparietal diameter, abdominal circumference and femur length as a comprehensive test for the prediction of discordancy. Methods: The sets of twins were studied with real-time ultrasonography for morphometric measurements and with duplex Doppler velocimetry for the S/D ratio of the umbilical artery in third trimester. The following cutoff values were used to indicate abnormal test results: Δ biparietal diameter > 6 mm, Δ abdominal circumference > 20 mm, Δ femur length > 5 mm, Δ estimated fetal weight > 15% and Δ systolic/diastolic ratio > 15%. Discordancy was identified when the birth weight difference exceeded 15%. Results: Among the 52 sets of twin pregnancies studied, 40 sets of twins fulfilled the study criteria. Thirteen sets of twins were discordant (32.5%) The mean gestational age at delivery was 37.15 ± 2.24 weeks (range 28-41 weeks). The diagnostic accuracy provided by ultrasonographic morphometries was not significantly different from that provided by umbilical Doppler velocimetry. Overall the best predictors appeared to be the presence of either Δ systolic/diastolic ratio > 15% or Δ estimated fetal weights > 15% with sensitivity and specificity values of 92% and 70%, respectively. Conclusion: Real-time ultrasonography combined with umbilical artery velocimetry is useful in predicting discordant twins.